An electrophoretic display is a flexible display having many attributes of a paper document. For example, it can look like paper, have ambient light valve behavior like paper (i.e. the brighter the ambient light, the more easily it may be seen), be flexible like paper, be carried around like paper, be written on like paper, be copied like paper, and have nearly the archival memory of paper.
Encapsulated electrophoretic displays typically consist of a polymeric binder surrounding ink capsules. The ink capsules or “electrophoretic ink” have electrophoretic particles and a liquid within. The particles are of two types, one type that substantially reflects light and another type that absorbs light. A pair of electrodes is located adjacent the binder to apply an electric field. Application of one electric field causes the particles to orient so that the capsules reflect light. Application of another electric field causes the particles to orient so that the capsules absorb light.
In order to respond to the electric field, the electrophoretic particles are charged. Problems arise, however, because conventional electrophoretic ink requires a complex mixture of ionic charge additives and ionic charge control agents in addition to the pigments, dispersants, and solvents. Moreover, the presence of those ionic additives results in a highly charged electrophoretic ink that requires a high switching field to move the particles within the capsules.
Thus, there is a need to overcome these and other problems of the prior art to provide an electrophoretic ink that can be used in an electrophoretic display having a low switching field and a fast response time.